Question

(a) How does the amperometric glucose monitor in Figure 7-12 work? b) Why is a mediator advantageous in the glucose monitor? c) How does the coulometric glucose monitor in Figure 17-14 work? (d) Why does the signal in the amperometric measurement depend on the temperature of the blood sample, whereas the signal in coulometry is independent of temperature? Do you expect the signal to increase or decrease with increasing temperature in amperometry?

(e) Glucose$\left(C_6{H}_{12}{O}_6\$,FM180.16\right)$is present in normal human blood at a concentration near 1g/L How many microcoulombs are required for complete oxidation of glucose in 0.300$\mathit{\mu }\mathit{L}$ of blood in a home glucose monitor if the concentration is 1.00g/L ?

Short answer

(a)When a drop of blood is placed on the strip, the glucose in the blood is transformed to gluconolactone, lowering the mediator. When a voltage of is applied to the carbon electrode, re-oxidation in the decreased mediator happens. The cureent affects the rate of oxidation of the mediator between the two electrodes. The rate at which mediators are oxidised is proportional to the amount of glucose and other metabolites in the bloodstream.

(b) Because the mediator's concentration is constant, fluctuations in electrode current due to changes in glucose concentration are unaffected. The interference of other species in blond is reduced by lowering the electrode voltage of the oxidation mediator.

(c)(c) A coulometric sensor can calculate the number of electrons required to oxidise glucose in a blood sample.

(d)(d) The blood temperature rises as the current increases. The number of electrons emitted during oxidation is measured using coulometry. Independent of temperature, glucose emits two electrons per molecule. Furthermore, the coulometric signal is unaffected by temperature.

(e) (e) The amount of current required to maintain constant glucose levels is

$Q=nF=left\left(3.33times10-9right\right)\left(96485C/mol\right)=321muC$

Step-by-step solution

Concept used

It is necessary to discuss the method of using an amperometric glucose monitor to monitor glucose levels.

Step 2:

(a)

The procedure of using an amperometric glucose monitor to measure glucose levels.

A test strip with two carbon electrodes and a reference electrode is included in an amperometric glucose monitor (silver-silver chloride). The carbon electrode is covered with a mediator and glucose oxidase. When a drop of blood is placed on the strip, the glucose in the blood is oxidised to gluconolactone, and the mediator is decreased. When a potential of is applied to the carbon electrode, re-oxidation in decreased mediator occurs. Between both electrodes, the rate of oxidation of the mediator is precisely proportional to the cureent. The rate of oxidation of mediator is proportional to the strength of glucose and other species in blood. The second indicator electrode contains simply mediator and no glucose oxidase. Current measurement between two points.

Step 3:

(b)

The advantages of using a glucose monitor with a mediator.

The oxidation rate of glucose, which is dependent on the quantity of oxygen in the blood, is affected by the absence of mediator. Because of the low current, the monitor displays a low glucose concentration when the oxygen concentration drops. A mediator, such as dimethylferrocene, can replace oxygen in the oxidation of glucose, resulting in a reduction at the indicator electrode. Because the concentration of the mediator is constant, changes in electrode current owing to changes in glucose concentration are unaffected. The interference of other species in blond is reduced by lowering the electrode voltage of the mediator for oxidation.

Step 4:

(c)

The procedure for using a coulnmetric glucose monitor to measure glucose levels.

Glucose oxidase, which replaces glucose dehydrogenase, does not need oxygen as a reactant. It oxidises glucose by reducing the PQQ cofactor to $PQQ{H}_2$.

By oxidising the $PQQ{H}_2$to PQQ the polymer chain creates PQQ .Electrons are exchanged from$O{s}^{2+}$ to $O{s}^{3+}$It can reach the carbon electrode through electron migration. The coulometric sensor can calculate the amount of electrons necessary to oxidise glucose in a blood sample.

Step 5:

(d)

The signal's amperometric measurement dependent.

Amperometry is used to quantify the current generated when glucose is oxidised by an enzyme. The rate of oxidation is proportional to the amount of current flowing. The rate of a chemical reaction is proportional to its temperature in general. As a result, current can raise the blood temperature as it rises. The number of electrons released during oxidation is determined via coulometry. Glucose, regardless of temperature, expels two electrons per molecule. Furthermore, the coulometric signal is unaffected by temperature.

Step 6:

(e)

A test strip with two carbon electrodes and a reference electrode is included in an amperometric glucose monitor (silver-silver chloride). The carbon electrode is covered with a mediator and glucose oxidase. When a drop of blood is placed on the strip, the glucose in the blood is oxidised to gluconolactone, and the mediator is decreased. When a potential of 0.2V is applied to the carbon electrode, re-oxidation in decreased mediator occurs. Between both electrodes, the rate of oxidation of the mediator is precisely proportional to the cureent. The rate of oxidation of mediator is proportional to the strength of glucose and other species in blood. The second indicator electrode contains simply mediator and no glucose oxidase. The strength of the species other than the reference electrode and the indication electrode two is used to measure the current between them.

The current required to monitor glucose levels at a fixed concentration is$321\mu C$

To calculate: The amount of current needed to keep track of glucose levels at a certain concentration.

1.00g of glucose = 5.55mMGlicose

$0.300\times {10}^{-6}L$has 1.665nmol glucose

During oxidation, glucose releases two electrons per molecule, regardless of temperature.

$2\times 1.665nmol=3.3nmol$electrons are liberated.

$Q=nF=left\left(3.33times10-9right\right)\left(96458C/mol\right)=321muC$